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Determination of the strength of L-type corner joints obtained from wood-based board materials using different joining techniques.

Abstract

Flat pack (ready-to-assemble, knockdown) furniture has become the most extensive furniture model produced with the development of wood-based board materials technology. It is especially preferred in the building industry as a model suitable for mass production. In this study, the resistances of dowels and screws, which are used in a widespread manner as joining material at the corners of ready-to-assemble furniture, were investigated against tensile and compression resistances in the diagonal direction. Chipboard (CB), medium-density fiberboard, and gaboon mahogany plywood (GMP), 14, 16, and 18 mm thick, were used in this study. Dowel + screw, screw, screw + polyvinyl acetate (PVAc) adhesive, and screw + polyurethane (PUR) adhesive joining were implemented for the L-type corner models obtained from wood-based board materials. According to the results obtained, the highest moment-carrying capacity values in the L- type corner joining were provided in the 18-mm GMP board joined with screw + PVAc adhesive and screw + PUR adhesive for both tests. The joining made without adhesive and the CB materials produced the lowest moment-carrying capacity values.

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Furniture should be designed so that production, from economical materials, is simple and practical and done in a manner that will create interest from the perspective of aesthetics and function. Furniture endurance design and analysis is a new concept and is still not implemented seriously in many countries. Up until the middle of the 1950s, furniture was not analyzed structurally despite the fact that furniture was defined as a structural system. Instead, past experience and aesthetics were the factors considered in the determination of element measurements and joinings (Erdil 1998). It is necessary to solve problems related to security, usability, and dimensions when designing furniture. The structure or system should show resistance of materials and construction to mechanical influences (Altinok 2003).

As the demand for flat-pack furniture in the furniture sector has increased flat-pack furniture production has also increased to the same extent. Flat-pack furniture has unique design and production techniques (Yerlikaya 2013b). Generally, L- and T-type elements are used in testing the joining for flat-pack furniture systems. The connections of the system are in the direction of the flat surface axes, whereas the tensile, bending, and shearing are in the direction of the flat surface diagonals and remain under the influence of torsion loads. Flat-pack furniture should be able to display resistance during use against the probable effects of these external loads (Altinok 2003).

Wood and wood-based materials constitute an important component for the design of furniture construction. The behavior against physical and mechanical effects of the materials included in the formation of furniture products should be known in advance and provide technical, aesthetic, and economic benefits to the designer, producer, and user. For both the design and the scientific activities based on this, data are used for the physical and mechanical attributes of the materials and the resistances of the joining (Efe 1994). Consequently, in addition to testing the joining system for flat-pack furniture, the materials constituting the furniture have been examined in many studies.

Zhang and Eckelman (1993a, 1993b) determined that as the dowel diameter and dowel length increase in chipboards produced with a single-dowel flat-pack corner joining element, their resistance increases; in cases where a different number of dowels are used, the distance between the two dowels should be 7.5 cm for the highest resistance. Efe and Kasai (2000) determined that using fiberboard was superior to using chipboard in flat-surface furniture production and that of the adhesives used, polyvinyl acetate (PVAc) produced the best results. Ors et al. (2001) stated that the polyurethane-based desmodur--vinyl trie ketonol acetate adhesive was the most successful with laminated medium-density fiberboard (MDF LAM) and 4 by 50-mm screws performed the best in the tensile resistance tests conducted on furniture corner joining. Efe and Imirzi (2008) determined that adhesive-screw experimental specimens produced from plywood and MDF materials in flat-pack furniture had a higher moment-carrying capacity against the diagonal tensile force. Tankut and Tankut (2010) stated that the side-band thickness in flat-pack furniture was effective and that 0.4-mm melamine side-band MDF LAM boards provided the best diagonal tensile resistance. Altinok et al. (2009) discovered that the dowel plus foreign strip of wood joining implemented together in flat-pack furniture produced from chipboards covered with melamine showed a better diagonal tensile and pressure resistance than when the joinings were made separately. Simek et al. (2010) determined that minifixed joinings strengthened the dowels to a significant extent without adhesive in flat-pack furniture. Yerlikaya (2013b) studied the resistance effects of a different number of dowels and minifixes in flat-pack furniture and showed that the highest bending moment value was in the joinings with two minifixes plus two dowels. Tankut (2006) carried out a study to determine the bending moment resistance of corner joints connected with different types of ready-to-assemble (flat-pack) fasteners so that the structure can safely resist the loads imposed on them in service. The fastener types included minifix cam-tightened mechanical connectors, rafix cam-tightened mechanical connectors, a corner fitting, a pipe-type fitting, a trapez connector with metal parts, and a trapez connector with plastic parts (known as corner block connectors). In both tension and compression tests, results also indicate that the joints constructed with MDF and the trapez connector with metal parts produced the highest resistance values; the rafix joints constructed with particleboard were the weakest joints evaluated.

In recent studies, different materials were tested for their ability to increase the diagonal resistances of flat-pack furniture. Yerlikaya (2013a) attempted to use glass-fiber fabric as a support in dowel joinings. It was found that dowel joinings supported with glass-fiber fabric implemented together in the internal and external parts of L-type corner joinings had a better diagonal tensile resistance compared with the unsupported, plain dowel joinings.

With the data obtained from this technological study, it will be possible to determine more reliably which material should be used where and which connection technique should be implemented on which material. In this study, the moment-carrying capacities were determined against the tensile resistances and the compression resistances of experimental specimens joined with different screw techniques that were prepared from wood-based board materials commonly used in the production of furniture. Thus, suggestions are made for the most suitable variety of material and joining form for tensile and compression resistances in the production of flat-pack construction furniture, which is the most suitable furniture production type for mass production.

Experimental

Materials

Boards.--The wood-based board materials used in the experiments included chipboard (CB), MDF, and gaboon mahogany plywood (GMP; Aucoumea klaineana) with thicknesses of 14, 16, and 18 mm according to TS 64-5 (EN 622-5; Turkish Standards Institution [TSE] 1999) and TS 4645 (EN 636; TSE 2005). Some physical and mechanical properties of wood-based materials are given in Table 1.

Adhesive.--PVAc and polyurethane (PUR) adhesives were used in the formation of the test specimens. PVAc is preferred because of its widespread use in the production of armchair frameworks and its attributes, which permit use in the cold and include facilitating spreading, rapid hardening, lack of odor, and fire resistance. PUR is used because of its good cohesion resistance; its elastic structure; its resistance against hot water, oil, and chemical substances; and its ability to enter into a reaction at room temperature (Burdurlu 1994).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Dowels and screws.--Dowels with threaded bodies having a diameter of 8 mm and lengths of 39, 41, and 43 mm were used in the experiments. Dowels were prepared from beechwood with the characteristics stated in the TS 4539 standard (TSE 1983; Fig. 1).

It is stated in the literature that the entrance depth of the dowel from the edge should be a minimum of 3.5 times the diameter of the dowel while not exceeding 90 percent of the thickness of the board on the surface (Norvydas 2004). Accordingly, it was calculated that the depth of entering from the surface was 11 mm for the 14-mm-thick board, 13 mm for the 16-mm-thick board, and 15 mm for the 18-mm-thick board and that the depth of entering from the edge for all three board thicknesses was 28 mm.

Four-millimeter-diameter, 50-mm-long Phillips screws were used in the experiments in accordance with the TS 61 standards (TSE 1978); these screws are used especially as connection elements in furniture joining produced from wood composite boards. The bottom diameter (root) of the thread of the Phillips screw used was 2.4 mm, and the pitch screw thread was 1.8 mm (Fig. 2).

Two screws were used for each test specimen. Pilot holes were opened on the opposite element with a diameter of 3 mm and a depth of 32 mm in the screwing processes. In the joinings with screws, it was proposed that pilot holes be opened to provide better joining (Forest Products Laboratory 1999).

[FIGURE 4 OMITTED]

Methods

Preparation of the test specimens.--Every test specimen was composed of two elements, labeled A and B. The perspective appearance and the measurements of the test specimens prepared are shown in Figure 3. All of the specimens obtained were conditioned at 20[degrees]C [+ or -] 2[degrees]C and 65 [+ or -] 5 percent relative humidity so that they could reach the equilibrium moisture content.

In the test specimens, the centers of the dowel holes were arranged symmetrically and exactly at the center in a manner that would be 32 mm in from the edges in the broadness direction of the piece's cross section and in a manner that would be exactly at the center axis in the thickness direction. The centers of the screw holes are shown in Figure 4.

[FIGURE 5 OMITTED]

Test methods and moment calculation.--The force carrying form, the moment arm distances, and the test specimen measurements for the diagonal tensile and compression resistance tests are shown in Figure 5. Diagonal resistance tests were carried out with a 4-ton universal test device according to the ASTM D1037 (ASTM International 2002) method (Fig. 6).

The moment force in the diagonal tensile tests ([M.sub.t]) was calculated with Equation 1:

[M.sub.t] = [F.sub.max]/2 x [L.sub.t] (Nm) (1)

[FIGURE 6 OMITTED]

The moment force in the diagonal compression tests (Mc) was calculated with Equation 2:

[M.sub.c] = [F.sub.max] X [L.sub.c] (Nm) (2)

where

[M.sub.t] and [M.sub.c] = moment (Nm),

[F.sub.max] = maximum force at the moment of breaking (N), and

L = arm of moment (m).

[FIGURE 7 OMITTED]

Test configuration.--In the tests, three different wood-based board materials (CB, MDF, and GMP), three different board thicknesses (14, 16, and 18 mm), four different joining techniques (dowel + screw, screw, screw + PVAc adhesive, and screw + PUR adhesive), and five specimens from every combination were prepared for a total of 180 (3 X 3 X 4 X 5 = 180) diagonal tensile specimens and a total of 180 diagonal compression specimens.

Evaluation of the data.--The effects of board type, board thickness, and construction type and the dual and triple interactions of these factors on the moment-carrying capacity of L-type corner joining in flat-pack furniture were determined with multiple analysis of variance (ANOVA). The least significant difference test was applied for the differences in the analysis for the level of significance among the groups that emerged as statistically significant according to a level of reliability of P < 0.05. Thus, the board type, thickness, and construction type from among the factors tested were determined by being separated into homogeneous groups according to the sequences of success between each other. Figure 7 shows of failure modes of test specimens for connection joints subjected to tension and compression moment.

Results and Discussion

The average diagonal tensile and compression moment resistance values obtained according to the type of material, the board thickness, and the joining techniques are given in Table 2. As can be seen from Table 2, the highest moment resistances were obtained in the specimens with 18-mm GMP boards joined with screw + PVAc adhesive in the diagonal tensile resistance tests and in the specimens with 18-mm GMP boards joined with screw + PUR adhesive in the diagonal compression resistance tests.

Using the values from Table 2, an ANOVA was made with the objective of determining whether the type of material, the board thickness, and the joining technique have a meaningful influence on both diagonal tensile and diagonal compression resistances (Table 3). According to the results of the multiple ANOVA, the effects on the moment-carrying capacity values obtained as a result of the type of material, board thickness, and joining technique for the diagonal tensile resistance tests on the L-type corner joinings were found to be statistically significant with an error probability of 0.05. In the same manner, the results of the ANOVA for the dual and triple interactions are also significant. A comparison of the effects of type of material and board thickness on the moment-carrying capacity is given in Table 4.

According to Table 4, as a result of the diagonal tensile resistance, it was determined that the test specimens produced with GMP had the highest moment-carrying capacity and 11 percent higher resistance than the specimens produced with MDF. Furthermore, of the boards used, the 18-mm-thick test specimens had the highest values, and it was observed that they had 15 percent higher resistance than the 16-mm-thick specimens. According to the joining technique, the test specimens produced with screws + PUR showed the highest carrying capacity and produced a 17 percent better result than the specimens prepared with screws + PVAc.

As a result of the diagonal compression resistance in Table 4, it was determined that the test specimens produced with GMP had the highest moment-carrying capacity and had 13 percent higher resistance than the specimens produced with MDF. The 18-mm-thick test specimens had the highest values, and they had 20 percent higher resistance than the 16-mm-thick specimens. The specimens produced with screws + PVAc had the highest values and they had 6 percent higher resistance than the specimens prepared with screw + PUR. The fixed joining produced using adhesive had a higher moment-carrying capacity than flat-pack joining produced without adhesive.

Rajak and Eckelman (1996) reported that the bending resistance of corner joints was essentially directly proportional to the number of fasteners used, i.e., the bending resistance of a two-fastener joint was twice as strong as a single-fastener joint. These results are also in agreement with the results of this study.

A comparison of the effects on the moment-carrying capacity of the joinings by the dual interaction of type of material and board thickness is given in Table 5. According to the diagonal tensile resistance in Table 5, the highest moment-carrying capacity was produced in the 18-mm-thick GMP. Also, the fact that the next best result was observed in the 16-mm-thick rather than the 18-mm-thick MDF boards is significant. The best moment-carrying capacity for the diagonal compression resistance was produced in 18-mm-thick GMP.

The results found for CB are some of the most important ones obtained in this study, as this material is used the most in the production of flat-pack furniture. Wang (1984) found that bending resistance of corner joints constructed with CB was strongly related to board density. Tankut (2006) stated that laminated MDF corner joints were an average of 22 percent stronger than laminated particleboard corner joints in both tension and compression tests. These results are also in agreement with the results of this study. In this situation, it is proposed that GMP and MDF boards should be used instead of CB in the production of load-carrying flat-pack furniture.

A comparison of the effects on the moment-carrying capacities for the joinings of the dual interactions of type of material and joining technique is given in Table 6. According to the diagonal tensile resistance in Table 6, the highest moment-carrying value was observed in the MDF boards joined with screws + PUR and in the GMP boards joined with screws + PVAc. The highest moment-carrying values for the diagonal compression resistance were produced in GMP boards joined with screw + PVAc.

The joining made without adhesive and the CB materials produced the lowest moment-carrying values. A comparison of the effects of the dual interactions of thickness of board and joining technique on the moment-carrying capacities of the joinings are given in Table 7.

According to Table 5, the highest moment-carrying values for both of the diagonal resistances were obtained in the test specimens produced with a thickness of 18 mm with the screw + PUR adhesive and with the screw + PVAc adhesive.

A comparison of the effects of the triple interaction among type of material, board thickness, and joining technique on the moment-carrying capacities of the joinings is given in Table 8 and shown in Figures 8 and 9.

According to the analysis values of the triple interaction, the highest moment-carrying value for the diagonal tensile resistance was produced in the test specimens obtained with 18-mm-thick GMP boards joined with screws + PVAc. The lowest moment-carrying values were determined in the test specimens obtained from the CB material produced in thicknesses of 14 and 16 mm and joined with screws without adhesive. The results of the diagonal compression resistance tests gave similar results. The highest moment-carrying value was produced in the 18-mm-thick GMP specimens joined with screws + PUR adhesive. The lowest moment-carrying value for the diagonal compression resistance was observed in the 14mm-thick CB specimens joined with screws + PUR adhesive.

These results show that the moment resistance in both tests increased as the board thickness increased. Also, the joining made with screws + adhesive had a higher moment-carrying capacity. In Tankut's (2006) study, the joints constructed with MDF and the trapez connector with metal parts produced the highest resistance values in both tests (31.796 Nm in the diagonal compression resistance and 75.201 Nm in the diagonal tensile resistance). This connector showed weaker resistance than the screw + adhesive combination, which had the highest resistance value in our study

[FIGURE 8 OMITTED]

Conclusions

The aim of this study was to determine the most suitable joining application for fulfilling the function for a long period of time without damaging the structure against tensile and compression resistances that could emerge in response to the effect of loads that could be encountered for flat-pack furniture.

[FIGURE 9 OMITTED]

The 18-mm GMP boards showed the best resistance against the diagonal tensile and compression resistances. In production where tensile and compression resistances are important, the 18-mm board thickness should be preferred. Because the 18-mm-thick test specimens had the highest values, it was established that they had 15 percent higher resistance than the 16-mm-thick specimens.

CB, which is the most preferred material for mass production in the furniture industry, has shown weaker resistance than GMP and MDF boards in both of the diagonal resistances. Consequently, the use of CB cannot be proposed in the production of furniture for use in places where it could be subjected to tensile and compression resistances under the effect of a load.

The fixed joinings produced using adhesive showed higher tensile and compression resistances compared with the flat-pack joining produced without adhesive. Especially if strong joints against a load are desired, flat-pack joining rather than an adhesive should be used. Even if a statistically significant difference emerged between the screw + PVAc and the screw + PUR joining techniques, the diagonal tensile and compression resistance values were similar to each other. Consequently, no proposal can be made regarding the two adhesives.

The study should be further developed to determine the behaviors that could be encountered in response to the probable load effects of different materials and joinings on furniture. Finally, with the data obtained through different research, it will be possible to determine more reliably which material should be used where and which connection technique should be implemented on which material.

The authors are, respectively, Assistant Professor, Dept, of Wood Products Industrial Engineering, Faculty of Technol., Gazi Univ., Ankara, Turkey (himirzi@gazi.edu.tr). Associate Professor, Dept, of Materials and Materials Processing Technol., Denizli Vocational School of Technical Sci., Pamukkale Univ., Denizli, Turkey (kadirozkaya@pau.edu.tr [corresponding author]); and Professor, Dept, of Wood Products Industrial Engineering, Faculty of Technol., Gazi Univ., Ankara, Turkey (hasanefe@gazi.edu.tr). This paper was received for publication in August 2014. Article no. 14-00081.

doi: 10.13073/FPJ-D-14-00081

Literature Cited

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Table 1.--Some physical and mechanical properties. (a)

                     Density (g/[cm.sup.3])    Moisture content (%)

Type of material       Mean        CV (%)        Mean        CV (%)

14-mm CB                 0.64         2.56         5.09         5.09
16-mm CB                 0.66         1.68         5.06         5.06
18-mm CB                 0.61         6.36         5.06         5.06
14-mm MDF                0.75         2.81         4.64         4.64
16-mm MDF                0.79         0.98         4.86         4.86
18-mm MDF                0.70         1.16         4.98         4.98
14-mm GMP                0.50         1.70         6.73         6.73
16-mm GMP                0.57         2.06         5.90         5.90
18-mm GMP                0.47         0.89         6.48         6.48

                     Bending strength (%)           Modulus of
                                                  elasticity (%)

Type of material       Mean        CV (%)        Mean        CV (%)

14-mm CB                10.16        15.41        2.006        10.33
16-mm CB                11.18        23.05        2.293        18.56
18-mm CB                12.31        24.75        2.379        22.37
14-mm MDF               31.24         5.72        2.821         3.74
16-mm MDF               32.09        10.71        3.129         4.76
18-mm MDF               27.67         6.13        3.436         3.78
14-mm GMP               43.49        11.48        4.905         4.77
16-mm GMP               45.37         6.81        5.790        17.17
18-mm GMP               44.71         8.57        5.048         3.37

(a) CV = coefficient of variation; CB = chipboard; MDF = medium-
density fiberboard; GMP = gaboon mahogany plywood.

Table 2.--Moment-carrying capacity values obtained at the end of the
resistance tests. (a)

                                              Diagonal tensile
                                              resistance (Nm)

                                           Avg.
              Board                       moment
Type of     thickness      Joining      resistance
material      (mm)        technique        (Nm)       SD    CV (%)

CB          14          Dowel + screw       19.14    1.39    7.28
                        Screw               13.55    0.46    3.37
                        Screw + PVAc        26.77    0.68    2.56
                        Screw + PUR         29.67    1.82    6.15

            16          Dowel + screw       24.57    0.68    2.75
                        Screw               14.04    1.35    9.64
                        Screw + PVAc        37.01    0.90    2.44
                        Screw + PUR         41.48    1.35    3.26

            18          Dowel + screw       38.19    2.90    7.60
                        Screw               24.93    0.22    0.90
                        Screw + PVAc        69.43    0.89    1.29
                        Screw + PUR         54.92    3.57    6.50

MDF         14          Dowel + screw       32.90    0.91    2.77
                        Screw               28.71    1.14    3.97
                        Screw + PVAc        44.19    0.68    1.55
                        Screw + PUR         61.93    0.91    1.47

            16          Dowel + screw       53.28    3.38    6.35
                        Screw               38.93    0.45    1.16
                        Screw + PVAc        51.37    3.38    6.59
                        Screw + PUR        101.78    2.03    1.99

            18          Dowel + screw       53.02    2.68    5.05
                        Screw               30.93    1.79    5.77
                        Screw + PVAc        55.86    4.24    7.59
                        Screw + PUR         93.42    5.80    6.21

GMP         14          Dowel + screw       32.90    0.91    2.77
                        Screw               18.71    0.91    4.88
                        Screw + PVAc        62.58    1.82    2.92
                        Screw + PUR         70.32    1.82    2.59

            16          Dowel + screw       51.69    2.26    4.36
                        Screw               27.76    0.23    0.81
                        Vida + PVAc         84.55    2.48    2.94
                        Vida + PUR          78.81    0.23    0.29

            18          Dowel + screw       62.18    0.22    0.36
                        Screw               26.20    2.90   11.08
                        Screw + PVAc       107.62    5.58    5.18
                        Screw + PUR         98.79    1.12    1.13

                                           Diagonal compression
                                              resistance (Nm)

                                           Avg.
              Board                       moment
Type of     thickness      Joining      resistance
material      (mm)        technique        (Nm)       SD    CV (%)

CB          14          Dowel + screw       17.90    0.84    4.71
                        Screw               15.51    1.69   10.88
                        Screw + PVAc        20.28    1.69    8.32
                        Screw + PUR         13.72    0.42    3.07

            16          Dowel + screw       20.98    4.12   19.64
                        Screw               14.57    0.41    2.83
                        Screw + PVAc        19.81    2.47   12.48
                        Screw + PUR         22.14    3.30   14.89

            18          Dowel + screw       29.01    0.40    1.39
                        Screw               23.32    0.40    1.72
                        Screw + PVAc        44.93    0.40    0.90
                        Screw + PUR         42.66    0.40    0.94

MDF         14          Dowel + screw       36.99    1.69    4.56
                        Screw               29.23    0.42    1.44
                        Screw + PVAc        34.60    0.84    2.44
                        Screw + PUR         29.83    0.84    2.83

            16          Dowel + screw       44.28    2.47    5.58
                        Screw               34.96    0.00    0.00
                        Screw + PVAc        41.37    4.53   10.96
                        Screw + PUR         46.61    4.94   10.61

            18          Dowel + screw       49.48    1.21    2.44
                        Screw               31.85    1.61    5.05
                        Screw + PVAc        51.19    1.61    3.14
                        Screw + PUR         51.76    0.40    0.78

GMP         14          Dowel + screw       28.63    1.69    5.89
                        Screw               16.70    0.84    5.05
                        Screw + PVAc        60.85    0.00    0.00
                        Screw + PUR         49.51    2.95    5.96

            16          Dowel + screw       44.28    1.65    3.72
                        Screw               30.30    0.82    2.72
                        Vida + PVAc         57.68    2.06    3.57
                        Vida + PUR          48.94    5.77   11.79

            18          Dowel + screw       52.33    1.61    3.07
                        Screw               30.15    1.21    4.00
                        Screw + PVAc        61.43    2.41    3.93
                        Screw + PUR         64.27    2.01    3.13

(a) SD = standard deviation; CV = coefficient of variation; CB =
chipboard; PVAc = polyvinyl acetate; PUR = polyurethane; MDF =
medium-density fiberboard; GMP = gaboon mahogany plywood.

Table 3.--Multiple analysis of variance (ANOVA) results related to
the moment-carrying capacity effects for the type of material, board
thickness, and the joining technique.

                          Degrees
                            of        Total of       Avg. of
Sources of variance       freedom     squares        squares

Results related to diagonal tensile resistance (Nm)

Type of material (TM)       2        24,639.924     12,319.962
Thickness of board (TB)     2        15,855.557      7,927.779
TM x TB                     4         2,533.245        633.311
Joining technique (JT)      3        54,649.616     18,216.539
TM x TB                     6        13,490.031      2,248.338
TB x JT                     6         3,373.425        562.237
TM x TB x JT               12         2,233.678        186.140
Error                     144           744.384          5.169
  Total                   179       117,519.860

Results related to diagonal compression resistance (Nm)

TM                          2        15,364.762      7,682.381
TB                          2         6,729.611      3,364.805
TM x TB                     4           726.912        181.728
JT                          3         8,963.400      2,987.800
TM x TB                     6         3,712.474        618.746
TB x JT                     6         1,135.363        189.227
TM x TB x JT               12         1,593.688        132.807
Error                     144           683.137          4.744
  Total                   179        38,909.347

                                         Probability
                                          of error
Sources of variance         F value      (P < 0.05)

Results related to diagonal tensile resistance (Nm)

Type of material (TM)      2,383.2795      0.0000
Thickness of board (TB)    1,533.6177      0.0000
TM x TB                      122.5132      0.0000
Joining technique (JT)     3,523.9640      0.0000
TM x TB                      434.9379      0.0000
TB x JT                      108.7640      0.0000
TM x TB x JT                  36.0085      0.0000
Error
  Total

Results related to diagonal compression resistance (Nm)

TM                         1,619.3855      0.0000
TB                           709.2745      0.0000
TM x TB                       38.3068      0.0000
JT                           629.8048      0.0000
TM x TB                      130.4267      0.0000
TB x JT                       39.8876      0.0000
TM x TB x JT                  27.9947      0.0000
Error
  Total

Table 4.--Comparison of the moment-carrying capacities
according to type of material, board thickness, and joining
technique. (a)

                           Diagonal tensile       Diagonal compression
                           resistance (Nm)          resistance (Nm)

       Source              Mean         HG          Mean         HG

Type of material
  CB                      32.81          C         23.74          C
  MDF                     53.86          B         40.18          B
  GMP                     60.18          A         45.42          A

Board thickness (mm)
  14                      36.78          C         29.48          C
  16                      50.44          B         35.49          B
  18                      59.62          A         44.37          A
                        LSD [+ or -] 0.8191 Nm   LSD [+ or -] 0.7847 Nm

Joining technique
  Dowel + screw           40.87          C         40.87          C
  Screw                   24.86          D         25.18          D
  Screw + PVAc            59.93          B         43.57          A
  Screw + PUR             70.12          A         41.05          B
                        LSD [+ or -] 0.9458 Nm   LSD [+ or -] 0.9061 Nm

(a) HG = homogeneous group; CB = chipboard; MDF = medium-density
fiberboard; GMP = gaboon mahogany plywood; LSD = least significant
difference test; PVAc = polyvinyl acetate; PUR = polyurethane.

Table 5.--Comparison of the effects on moment-carrying capacities
according to the dual interaction of type of material and board
thickness (14, 16, and 18 mm). (a)

                   Diagonal tensile resistance (Nm)

                 14 mm             16 mm             18 mm
Type of
material      Mean      HG      Mean      HG      Mean      HG

CB           22.28      G      29.27      F      46.87      D
MDF          41.93      E      61.34      B      58.31      C
GMP          46.13      D      60.70      B      73.70      A
                        LSD [+ or -] 1.419 Nm

                      Diagonal compression resistance (Nm)

                 14 mm             16 mm             18 mm
Type of
material      Mean      HG      Mean      HG      Mean      HG

CB           16.85      H      19.37      G      34.98      E
MDF          32.66      F      41.81      C      46.07      B
GMP          38.92      D      45.30      B      52.04      A
                        LSD [+ or -] 1.359 Nm

(a) HG = homogeneous group; CB = chipboard; MDF = medium-density
fiberboard; GMP = gaboon mahogany plywood; LSD = least significant
difference test.

Table 6.--Comparison of the moment-carrying capacities according to
the dual interaction for type of material and joining technique (a)

                    Diagonal tensile resistance (Nm)

               Dowel + screw               Screw
Type of
material      Mean         HG         Mean         HG

CB            27.30         H         17.51         J
MDF           46.40         D         32.86         G
GMP           48.92         C         24.22         I
                        LSD [+ or -] 1.638 Nm

                    Diagonal tensile resistance (Nm)

                Screw + PVAc             Screw + PUR
Type of
material      Mean         HG         Mean         HG

CB            44.40         E         42.02         F
MDF           50.47         C         85.71         A
GMP           84.92         A         82.64         B
                        LSD [+ or -] 1.638 Nm

                 Diagonal compression resistance (Nm)

                Dowel + screw               Screw
Type of
material      Mean         HG         Mean         HG

CB            22.63         H         17.8          I
MDF           43.58         C         32.01         E
GMP           41.75         D         25.72         G
                        LSD [+ or -] 1.569 Nm

                 Diagonal compression resistance (Nm)

                Screw + PVAc             Screw + PUR
Type of
material      Mean         HG         Mean         HG

CB            28.34         F         26.17         G
MDF           42.39        CD         42.73        CD
GMP           59.99         A         54.24         B
                        LSD [+ or -] 1.569 Nm

(a) PVAc = polyvinyl acetate; PUR = polyurethane; HG = homogeneous
group; CB = chipboard; MDF = medium-density fiberboard; GMP = gaboon
mahogany plywood; LSD = least significant difference test.

Table 7.--Comparison of the moment-carrying capacities according to
the dual interactions of thickness of board and joining technique
(a)

                   Diagonal tensile resistance (Nm)

Board           Dowel + screw               Screw
thickness
(mm)           Mean         HG         Mean         HG

14             28.31         H         20.32         I
16             43.18         G         26.91         H
18             51.13         F         27.35         H
                         LSD [+ or -] 1.638 Nm

                   Diagonal tensile resistance (Nm)

Board            Screw + PVAc             Screw + PUR
thickness
(mm)           Mean         HG         Mean         HG

14             44.51         G         53.97         E
16             57.64         D         74.02         C
18             77.64         B         82.38         A
                         LSD [+ or -] 1.638 Nm

                   Diagonal compression resistance (Nm)

Board           Dowel + screw               Screw
thickness
(mm)           Mean         HG         Mean         HG

14             27.84        FG         20.48         H
16             36.51         D         26.61         G
18             43.61         B         28.44         F
                         LSD [+ or -] 1.569 Nm

                   Diagonal compression resistance (Nm)

Board            Screw + PVAc             Screw + PUR
thickness
(mm)           Mean         HG         Mean         HG

14             38.58         C         31.02         E
16             39.62         C         39.23         C
18             52.52         A         52.90         A
                         LSD [+ or -] 1.569 Nm

(a) PVAc - polyvinyl acetate; PUR = polyurethane; HG = homogeneous
group; LSD = least significant difference test.

Table 8.--Comparison of the moment-carrying capacities according to
the triple interactions of type of material, board thickness, and
joining technique. (a)

                                Diagonal tensile resistance (Nm)

              Board         Dowel + screw               Screw
Type of     thickness
material      (mm)        Mean         HG         Mean         HG

CB             14       19.14       U           13.55#      V#
               16       24.57       T           14.04#      V#
               18       38.19       N           24.93       ST
MDF            14       32.90       O           28.71       PQR
               16       53.28       UK          38.93       MN
               18       53.02       JK          30.93       OP
GMP            14       32.90       O           18.71       U
               16       51.69       K           27.76       QRS
               18       62.18       H           26.20       RST
                                    LSD [+ or -] 2.837 Nm

                                Diagonal tensile resistance (Nm)

              Board              Screw + PVAc         Screw + PUR
Type of     thickness
material      (mm)        Mean         HG         Mean         HG

CB             14        26.77      RST         29.67       PQ
               16        37.01      N           41.48       LM
               18        69.43      G           54.92       IJ
MDF            14        44.19      L           61.93       H
               16        51.37      K           101.8       B
               18        55.86      1           93.42       D
GMP            14        62.58      H           70.32       G
               16        84.55      E           78.81       F
               18       107.60#     A#          98.79       C
                                    LSD [+ or -] 2.837 Nm

                              Diagonal compression resistance (Nm)

              Board         Dowel + screw               Screw
Type of     thickness
material      (mm)        Mean         HG         Mean         HG

CB             14       17.90       PQ          15.51       QRS
               16       20.98       NO          14.57       RS
               18       29.01       M           23.32       N
MDF            14       36.99       K           29.23       LM
               16       44.28       HI          34.96       K
               18       49.48       EF          31.85       L
GMP            14       28.63       M           16.70       QR
               16       44.28       HI          30.30       LM
               18       52.33       D           30.15       LM
                                    LSD [+ or -] 2.718 Nm

                              Diagonal compression resistance (Nm)

              Board          Screw + PVAc            Screw + PUR
Type of     thickness
material      (mm)        Mean         HG         Mean         HG

CB             14       20.28       OP          13.72#      S#
               16       19.81       OP          22.14       NO
               18       44.93       HI          42.66       IJ
MDF            14       34.60       K           29.83       LM
               16       41.37       J           46.61       GH
               18       51.19       DEF         51.76       DE
GMP            14       60.85       B           49.51       EF
               16       57.68       C           48.94       FG
               18       61.43       B           64.27#      A#
                                    LSD [+ or -] 2.718 Nm

(a) Bold values indicate the highest and lowest values. PVAc =
polyvinyl acetate; PUR = polyurethane; HG = homogeneous group; CB =
chipboard; MDF = medium-density fiberboard; GMP = gaboon mahogany
plywood; LSD = least significant difference test.

Note: Values indicate the highest and lowest values are indicated
with #.

Figure 3.--The perspective appearance and measurements of the L-type
joining test specimens.

A and B Piece Measurements

  a        b        c        d

14 mm   200 mm   186 mm   320 mm
16 mm   200 mm   184 mm   320 mm
18 mm   200 mm   182 mm   320 mm
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Author:Imirzi, Hasan Ozgur; Ozkaya, Kadir; Efe, Hasan
Publication:Forest Products Journal
Date:Jul 1, 2016
Words:6395
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